The field of art to which this invention pertains is radiation curable compositions.
Due to environmental concerns and the high cost of solvents, commercial interest in radiation curable compositions is constantly increasing. Legislation which restricts the amount of solvent and other pollutants that can be vented to the atmosphere is one reason for this increased interest. Other reasons are the concerns expressed by unions and individuals over the possible toxic effects of prolonged exposure to volatile organic materials and also the high cost of petroleum derived solvents. Generally, radiation curable systems are essentially 100 percent reactive systems, i.e., substantially all of the components react to produce the final product. Such systems can be cured by exposure to medium to high energy ionizing radiation or to actinic radiation in the presence of photoinitiators.
Various types of ethylenically unsaturated compounds have been used in making radiation curable compositions. Examples of such compounds include acrylated epoxide resins, such as those described in U.S. Pat. Nos. 3,676,398, 3,770,602, 4,072,529 and 4,511,732. Acrylated urethanes, such as those described in U.S. Pat. Nos. 3,700,643 and 4,511,732, have also been used in radiation curable compositions. Other acrylated urethane compounds made from a poly(alkylene oxide polyol), a polyisocyanate and an unsaturated active hydrogen-containing compound are described in U.S. Pat. Nos. 4,133,723 and 4,188,455. These urethane compounds are said to be radiation curable in the presence of oxygen.
Unsaturated polyesters based on maleic anhydride or fumaric acid have been used in combination with styrene and later with multifunctional acrylates as ultraviolet cured wood fillers and topcoats. The cure rates of these polyesters are slow due to the relatively unreactive nature of the unsaturated polyester internal double bond. In order to obtain faster curing compositions, acrylated polyesters have been developed. As described in U.S. Pat. No. 4,206,025, such polyesters are generally made by the direct esterification of a polyester polyol with acrylic acid.
Although acrylated polyesters are faster curing than unsaturated polyesters, they still cure slower than epoxy acrylates due to the absence of the beta-hydroxy group which has been shown to minimize the effects of oxygen inhibition during ultraviolet (UV) cure. The manufacture of such polyester acrylates involves a two step esterification reaction that can be complex, thereby affecting productivity and cost.
U.S. Pat. Nos. 3,089,863 and 4,659,778 describe a one step process for preparing polyesters by addition polymerization involving the reaction of a polyol, a dibasic acid anhydride and a wide range of monoepoxides. When the monoepoxide is glycidyl acrylate, a beta-hydroxy acrylic ester is formed.